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Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 7d

In the hydrocarbon
Diagram of a hydrocarbon showing bond angles labeled A, B, C, D, and E, highlighting 120° angles.
(d) Identify all the 120° bond angles in the molecule.

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Identify the regions in the molecule where the carbon atoms are sp2 hybridized, as these will have bond angles of approximately 120°.
Look at the diagram and locate the bond angles labeled A, B, C, D, and E.
Determine which of these angles are formed by sp2 hybridized carbons.
Recognize that sp2 hybridized carbons are typically found in double bonds or in a trigonal planar arrangement.
Identify the bond angles that are approximately 120° based on the molecular geometry and hybridization.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bond Angles

Bond angles are the angles formed between two adjacent bonds at a central atom in a molecule. They are crucial for understanding molecular geometry and the spatial arrangement of atoms. In hydrocarbons, bond angles can vary depending on the hybridization of the carbon atoms involved, with common angles being 109.5° for tetrahedral, 120° for trigonal planar, and 180° for linear geometries.
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Hybridization

Hybridization is the concept that describes the mixing of atomic orbitals to form new hybrid orbitals, which can explain the geometry of molecular bonding. In hydrocarbons, carbon atoms can undergo sp, sp², or sp³ hybridization, leading to different bond angles. For example, sp hybridization results in a linear arrangement with 180° angles, while sp² leads to trigonal planar arrangements with 120° angles.
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Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is determined by the number of bonding pairs and lone pairs of electrons around the central atom. Understanding molecular geometry is essential for predicting the bond angles and overall shape of the molecule, which is particularly relevant in hydrocarbons where multiple bond types (single, double, triple) influence the structure.
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Molecular Geometry with Two Electron Groups